Wick type evaporator

ABSTRACT

A device for vapor deposition containing as a vaporizer element, a wick formed of a lace-like body of graphite or carbides.

United States Patent 1191 1111 3,723,706

Van Amstel 1 Mar. 27, 1973 [54] WICK TYPE EVAPORATOR [56] References Cited Inventor: Johannes .llcobus ASICIIIS PINS 1 Van Amstel, Emmasingel, Eindhoven, Netherlands 2,597,195 5/1952 Smith ..219/274 X y 2,608,436 8/1952 Baughmam. ..219/274 X 1 Asslgnee: ip p i New 2,665,225 1/1954 c.6616 ..118/49 ux York, N.Y. 3,068,337 12/1962 Kuebrich et a1. ...1 18/49 X [22] Filed: Apr. 6, 1971 3,117,210 1 1964 Herb ..118/49 x 3,152,246 10/1964 Van Dcuren et a1. ..118/49 X 1 1 Appl- 1311793 3,362,915 1/1968 Micek ..1 18/49 x 3,413,239 ll/1968 Olstowski et al. ....252/425.5 X 3,627,191 12 1971 Hood, Jr ..117 121.2 [62] Division of Set. N0. 765,826, Oct. 8, 1968, Pat. No.

3,607,368. Primary Examiner-Morris Kaplan Attorney-Frank R. Trifari [30] Foreign Application Priority Data 061.. 10, 1967 Netherlands ..6713713 [571 ABSTRACT A device for vapor deposition containing as' -a [52] US. Cl ..219/274 vaporizer element, a wick formed Of a lace-like body [51] Int. Cl ..C23c 13/12, H0511 l/OO f graphite or carbides [58] Field of Selrcll ..1l8/48-49.5, 506;

219/273, 271, 274, 275; 239/44 -46; 2 Claims, No Drawings WlCK TYPE EVAPORATOR This application is a division of our copending US. Pat. application Ser. No. 765,826, filed Oct. 8, l968 and now US. Pat. No. 3,607,368.

The invention relates to the coating of substrates by vapor deposition.

,As is known, this is generally carried out in an atmosphere which is inert relative to the substance to be deposited in which, in order to check impediment of the vapor molecules on their way to the substrate, the gas pressure is chosen to be low and the method is usually carried out in a vacuum.

The vaporization of the substance to be deposited is usually effected by means of a vaporizer element which is heated by the passage of current.

According to some of the known methods, the sub stance is caused to vaporize on the surface of a heating element. A drawback hereof is that the substance can be present only in restricted quantities and hence the vapor deposition of thick layers or the continuous vapor deposition is not possible.

In other known methods this drawback is avoided by placing a large quantity of the substance to be vaporized directly inside or in a container inside a heating element which has the form of a helically wound filamentary body. However, a shadow effect of the heating body always occurs which hampers the obtaining of an even coating.

The use of a vaporizing element is also known to which the substance to be vapor-deposited is applied continuously from a container during the vaporization process (US. Pat. No. 2,665,227). In this method, an approximately horizontally arranged vaporizer element in the form of a rod is sued which is provided with a channel-like groove extending in the longitudinal direction in which the substance is allowed to flow from the container. This element is composed of a material which is readily wetted by the substance to be vapordeposited so that it is coated with the substance, all over its surface. For many applications, graphite was found to be a suitable material, if desired, converted superficially into a high-melting-point metal carbide.

A drawback of such vaporizer elements is that during use they have to be arranged approximately horizontally. In addition, the layer thickness of the substance to be vapor deposited in the groove is different from that on the further surface of the element. The result of this is a difference in vaporization at the area of the groove so that substrates arranged around the elements are coated in different thicknesses dependent upon their position.

The invention is based on the recognition of the fact that the above-mentioned drawbacks can be avoided by using an electrically conducting vaporizer element which is built up from a porous material.

According to the invention, a vaporizer element is used for this purpose, which is constructed from a lacelike body of graphite yarn.

Such a material is commercially available and may be obtained, for example, by carbonizing rayon yarns, which may be knitted or twined, at temperatures above approximately 2,000C.(See for example an Article by MoLindsey in Design Engineering of April 6, 1965 titled: Developments in Carbon and graphite Textiles."

F.o. Materials which advantageously can be used are sold by Morganite Research and Development Ltd. U.K. as graphite card grade 6301 G and 6303 C.

The invention relates to an apparatus for coating substrates by vapor-deposition from the surface of a vaporizer element built up from graphite and heated by the passage of current, characterized in that the substance to be vapor-deposited is taken up in a vaporizer element consisting of a lace-body which is built up from graphite yarn and is then heated at a temperature at which said substance vaporizes.

By the use of this apparatus a very even coating of the whole vaporizer surface can be obtained, which is a condition for obtaining an even deposition on sub.- strates arranged around the vaporizer. Any shadow effect of the material of which the element consists can be excluded by the fineness of the pores.

In this connection a vaporizer element is preferably used which is built up from yarns, the elementary strands of which have a thickness of under 20 microns.

The substance to be vaporized may be incorporated in the vaporizer element in comparatively large quantities. If very thick layers have to be vapor-deposited, or large numbers of substrates have to be coated in a continuous process however, it is of advantage to add a further quantity of the substance to the element during the vaporization process.

According to a useful embodiment of the invention a porous lace-like body is used which comprises a coaxial cavity. As a result of this it is possible to incorporate larger quantities of the substance to be vapor-deposited in the vaporizer.

Some substances, for example, copper, germanium and tin, do not react with the graphite material of the vaporizer. If such a substance is melted in the vaporizer, it penetrates through the pores in the wall to the outer surface on which an even layer is then formed. In this case it is recommended to use a hollow vaporizer element which can easily be filled with the material to be vaporized.

With substances, for example, chromium, which poorly wet graphite, it is of advantageous in order to obtain an even vaporization, to convert the graphite entirely or superficially into metal carbide. As is known, many of these carbides can withstand the influence of very high temperatures and are more easily wetted by various substances. For this purpose are to be considered the carbides of metals of the groups IVa, Va and Vla of the periodic system of elements, particularly zirconium carbide, and in addition aluminum carbide.

However, cases may also present themselves in which the graphite and the substance to be vapordeposited react with each other while forming carbides. This is the case notably in the above-mentioned carbide-forming metals. In itself this reaction is by no means objectionable because the carbide vaporizes at higher temperatures than the metals from which they are formed. If the carbides decompose at the vaporization temperature of the material, the vaporization may be continued after no free metal is present any longer in the vaporizer. The metal bound in carbide is then also vaporized and a graphite skeleton remains. This is the case, for example with aluminum carbide.

Of course it is possible with these metals which do react with graphite, to convert the graphite body previously entirely or superficially into a carbide of a metal other than the metal which is to be vaporized. For example, the graphite may be converted into zirconium carbide, as a result of which an element of a very large strength is obtained, which can be used repeatedly for vapor-deposition of metals, for example, cobalt and chromium.

The supply to the vaporizer of the substance to be vapor-deposited may be effected in a liquid and in a solid state, both prior to and during the vaporization.

Thus according to the invention a device for coating substrates by vapor-deposition comprises a container for melting the substance to be vaporized and a vaporizer element into which the molten substance flows said vaporizer element consisting of a lace-like body built up from yarns of graphite and/or a carbide. The molten substance may be made to flow into the vaporizer element by use of gravity or capillary action.

In some cases, for example, when molten silicon or germanium material is supplied to an element which is converted into silicon carbide, such a strong capillary action occurs that, if such an element is placed in the molten material with one end this material will be sucked up into it.

When filling with metal in the solid state it is recommended to use a vaporizer element which is provided with a coaxial cavity. The metal in the form of powder, grains or wire, can easily be provided in said cavity. As a continuous supply during the vaporization process, metal in the form of a wire is most suitable. This is the case also when replenishing the molten substance which is supplied to the vaporizer element through a container. 7

In order that the invention may be readily carried into effect, a few examples thereof will now be described in greater detail, with reference to the accompanying drawing in which FIG. 1 shows in perspective a hollow graphite lace and FIG. 2 shows a section of a part of a device for vapor-coating according to the invention. FIG. 3 shows a section of a device for vaporcoating according to the invention.

EXAMPLE 1 Two copper wires 2, thickness 0.5 mm, length 320 mm, are slid into a hollow graphite lace 1, length 400 mm, outside diameter approximately 2 mm, inside diameter approximately 1 mm, as shown on an exaggerated scale in FIG. 1 of the drawing, so that on either side approximately 40 mm of the lace is free from metal.

This element is arranged horizontally in a vacuum and heated by a current of 13 A. With an initial voltage of 20 V. For maintaining this current which is necessary for maintaining a vaporization temperature of approximately 2,000C, the voltage must gradually be increased to approximately 90 V.

The copper wires melt. The molten copper does not wet the graphite element but an even vaporization of copper around the element is obtained.

In this manner copper mirrors with an even thickness of l p. are deposited in approximately 20 min on glass substrates which are arranged at a distance of 80 mm from the element. The graphite lace was a material sold by Morganite Research and Development Ltd. as graphitecord grade 6301 G according to the manufacturer this as a plaited cord about 2 mm diameter. The electrical resistance is 0.45 0.69 Oper cm. at room temperature, falling to about half this value at l,500l,800C. The weight of the cord is approximately 1.3 gms/m.

EXAMPLE 2 A graphite lace as described in Example 1 is filled with 1.7 gms of germanium grains over a length of 300 By heating in a vacuum, the germanium which does not wet the graphite lace is caused to mold and vaporize in a vacuum.

This is carried out in a horizontal set-up with a current of 12 A at a voltage increasing from 50 to 130 V as a result of which a vaporization temperature of approximately 1,700C is reached.

Even germanium mirrors, thickness 2.2. microns, are obtained in this manner in approximately 30 minutes on glass substrates which are arranged at a distance of mm. In quite an analogous manner antimonly has also been processed to mirrors.

EXAMPLE 3 A densely braided graphite lace 3, length 400 mm, as shown in FIG. 2, is threaded through an aperture 4 in the bottom of a crucible 5 and secured there by means of a knot 6. Aluminum 7 is provided in the crucible 5 and is kept in the molten state at approximately 800C. As shown in FIG. 3 the crucible 5 is positioned in an oven 8. The lace 3 is brought under a weak tensile stress by the leaf springs 14 to which the lace 3 is connected through member 11 having an aperture 15 in which lace 3 is secured by means of a knot 12 and the means 13 for holding member 11. Substrate holders 10 are arrangedaround the lace 3. Electrical connections are made with spring 9 which is arranged between the crucible 5 and the inner wall of the electric oven 8 and the holding means 13. The device as shown in FIG. 3 is positioned in a vacuum chamber (not shown). The chamber is evacuated. The mass 7 consisting of aluminum is heated to a temperature of 800 C by means of the oven 8. The lace 3 is heated to approximately 2,000C with a current of 27 A with an initial voltage difference of 80 V between the springs 9 and the holding member 13. Aluminum is sucked up from the crucible and reacts with the graphite while forming aluminum carbide. At the same time free aluminum is taken up in the elements. With a current passage of A and a voltage of 8 V a temperature of approximately 1,200C is generated. On substrates which are arranged at a distance of 40 mm, aluminum mirrors, thickness 20 pt, are vapor-deposited in this manner in 20 minutes.

During the vaporization process, the aluminum in the element is replenished by a capillary sucking from the crucible. By supplying aluminum wire to the crucible the process can be made to be continuous.

If the vapor-deposition is continued without further supply of aluminum, not only does the free aluminum vaporize but also the aluminum which is bound in the carbide, and a graphite skeleton remains. Of course, the current must be reduced as soon as decomposition of the aluminum carbide begins to occur.

Silicon and germanium have been vaporized analogously from an element which is converted into silicon carbide. In these cases the vaporization is not continued up to decomposition of silicon carbide.

EXAMPLE 4 A rod of titanium, length 250 mm, thickness 2 mm, is slid into a hollow graphite lace as described in Example EXAMPLE 5 in a manner quite analogous to that described in example 4 a graphite lace is converted into a zirconium carbide element, the quantity of zirconium being chosen to be so that only a small excess of this metal remains.

The resulting hollow zirconium carbide element is filled with chromium in powder form and then heated in a vacuum to approximately l20 C by a current of 50 A with 20 V.

Chromium mirrors, thickness approximately 1 u, are

then obtained in 25 minutes on substrates which are arranged at a distance of mm.

In the same manner mirrors of cobalt are realized.

What is claimed is:

l. A device for coating substrates by vapor-deposition comprising in combination a container in which a substance to be evaporated can be melted, a vaporizer element consisting of a porous lace-like body built up from yarns of graphite or a carbide of a metal selected from metals of groups lVa, Va and Via of the periodic table of the elements said vaporizer element being positioned so as to receive the flow of molten substance from the container and means for electrically heating said vaporizer element to thereby effect vaporization.

2. A device according to claim 8 in which the vaporizer element consists of a lace-like body which is built up from yarns of a carbide chosen from the group consisting of the carbides of silicon, zirconium and titanium.

UNITED STATES PATENT OFFICE Page 1 of 3 CERTIFICATE OF CORRECTION 3,723,706 March 27, 1973 Patent No. Dated Johannes Jacobus Asuerus' Ploos Van Amstel Inventor(s) v It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, "2 Claims, No Drawings' 'shoul d read 2 Claims,'3 Drawings Figs. Insert FIGURES l, and 3, as part of Letters Patent, as shown on the attached sheets Column 6, lines 5 and 6, cancel "for coating substrates by vapor-deposition" 3 Column 6, line 10, after "from" insert the group consisting of the Column 6, line 11, "elements" should read elements,

Signed and Scaled this [SEAL] eleventh Day of May 1976 Arrest:

RUTH C. MASON C. MARSHALL DANN (mnmissimu'r IIau'mx aml Tradcmdrks A nesting Officer 

2. A device according to claim 8 in which the vaporizer element consists of a lace-like body which is built up from yarns of a carbide chosen from the group consisting of the carbides of silicon, zirconium and titanium. 